Paints and coatings are often used to protect a surface from corrosion, oxidation or other types of deterioration and to provide decorative effects.
An organic solvent-based (alkyd) paint or coating is a uniformly dispersed mixture ranging in viscosity from a thin liquid to a semi-solid paste and includes a film-forming polymeric binder, an organic solvent, pigment and other additives. The binder and the solvent collectively make what is known as the “vehicle.”
A latex or emulsion paint or coating is a uniformly dispersed mixture ranging in viscosity from a thin liquid to a semi-solid paste and includes a film-forming polymeric binder, water (solvent), pigment and other additives. The binder and the solvent collectively make what is known as the “vehicle.” Latex paints and coatings are popular consumer paints, as they are easy to apply, are usually easy to clean up, nonflammable, generally lack a disagreeable odor and can be used on both interior and exterior surfaces.
Pigments impart color to both alkyd and latex paints and coatings. They also can contribute to the opacity, durability and hardness of paint coatings. They can be added to paint in the form of dry pigment powders and/or pigmented tinting concentrate, e.g., a colorant composition, during paint manufacture at the paint plant. In addition, especially for consumer latex paints, they may be added in the form of pigmented paint tinting concentrates at the point of sale, such as at retail paint stores. Essentially, the consumer may choose a custom-made color of the paint by having the retailer add a colorant composition to a white or tintable base.
Pigments are ordinarily organic or inorganic dry powders that incorporate a mixture of primary particles, aggregates and agglomerates. Aggregates are primary pigment particles joined face-to-face, and agglomerates are primary pigment particles joined at an edge or a corner. For both industrial and consumer paints, whether solvent- or latex-based, the pigment preferably should be dispersed homogeneously throughout the paint. To properly be dispersed, pigments are usually wetted, deaggregated and deagglomerated in a vehicle. Dry pigments may be insoluble in organic solvents and water, which can necessitate wetting, deaggregation and deagglomeration before dispersion forces can take full effect and enable the production of a stable, colloidal pigmentary dispersion in the paint vehicle. The wetting or deaeration process can be physical in nature, as it may require that the vehicle or solvent displace air on the surface of the pigment particles. An ideal dispersion consists of a homogenous suspension of particles, after reducing the size of any aggregates and agglomerates.
The wetting process may be accomplished through the use of wetting agents, which typically are a type of surface-active agent or “surfactant.” As discussed, wetting involves incorporation of the pigment into the vehicle replacing pigment-air interfaces with pigment-vehicle interfaces. Surfactants facilitate bringing pigments into a dispersed state as a result of surface activity at the pigment-solution interface. In general, surfactant molecules can be composed of two segregated portions, one of which can have sufficient affinity for the carrier (organic or aqueous) to bring the entire molecule into a dispersed state. The other portion can be rejected by the carrier, because it has less affinity for the carrier than the carrier molecules have for each other. If the forces rejecting this group are sufficiently strong, the surfactant molecule will tend to concentrate at an interface, so that at least part of the area of the rejected group is not in contact with the carrier molecules. While some organic carriers may be good pigment wetting agents themselves, surfactants are typically added to alkyd paints to ensure thorough pigment dispersion throughout the paint vehicle. Water-based systems are usually poor wetting agents of dry pigments, and thus, latex paints often require the addition of surfactants for pigment dispersion.
Surfactants can also be used to temporarily stabilize the pigment dispersion from re-aggregating and re-agglomerating. Problems that occur with current available colorant compositions include (i) a separation or settling of the compositions into their components over time which can require periodic remixing or stirring, and (ii) an undesirable change in rheological profile of the paint when the colorant is added, i.e., the paint becomes too thick or too thin. The latter problem is particularly present when the base paint includes an associative thickener. Also, these compositions generally do not have low levels of volatile organic compounds (“VOC”), and/or they are not universal, e.g., they are not suitable for both alkyd and latex paints or coatings. Thus, there exists a need for colorant compositions that are non-settling or non-separating, have a low VOC and provide an advantageous rheological profile.